The dog nipped gently and immediately let go, it wasn't harmful, it was in play. The cat wasn't phased by it at all, didn't even flinch. Either way, the cat can very well teach the dog to not mess with it. One swipe with claw will get that pup to back down and know to not do it again. That of course is dependent on breed, but we're talking of a harmless Beagle here.
There's also no saying if this dog isn't trained by the owner to stop on command. My dog plays with my brothers cat but will stop when told to do so.

Read the cats body language, neither are bothered even slightly, they're comfortable with the dog and knows it's harmless.